Shampoos typically include surfactants, conditioners, and styling aids. However, surfactant residue, styling aid residue, and cationic build-up from conditioners cause hair to become dull, flat, and unmanageable. Although some shampoos can remove cationic build-up, they cause the hair to become frizzy, dry, and unmanageable. Therefore, there is a need for a shampoo which can remove dirt, oil, surfactant residue, conditioner residue, and styling aid residue that build up in hair, while leaving the hair in a non-stripped, non-drying, and conditioned state. The residue in hair is typically predominantly conditioner.
Additionally, the ingredients used in formulating a liquid shampoo and other liquid toiletries are often supplied in solid or powder form. Consequently, it is necessary to disperse these solids or powders in liquid solutions in order to formulate the shampoo or other liquid toiletry product.
Various dispersers and methods for dispersing solids into liquid solutions have been developed over the years. See, U.S. Pat. Nos. 3,256,181; 3,423,075; 3,606,270; 3,871,625; 3,998,433; 4,002,324; 4,092,738; 4,175,873; 4,239,396; 4,327,759; 4,453,829; 4,511,256; 4,767,217; 4,808,004; 4,850,702; 4,850,704; 4,955,723; 5,085,513; 5,322,357; 5,501,524; 5,540,499; and 5,599,102. For example, U.S. Pat. No. 5,085,513 describes an apparatus for continuously mixing a powder and a liquid together.
However, continuous or in-line processing methods are not well suited to the rapidly changing processing needs of the liquid toiletry industry because the equipment used to make a particular formula tends to be highly formula-specific. Thus, changes to a formula or attempts to make products having different formulas in continuous process equipment often give rise to significant modifications to the equipment used to make these formulas. Therefore, shampoos and other liquid toiletries are often produced by the more flexible batch processing method, where all of the processing steps are performed in one vessel known as a "batch reactor". These processing steps can include, for example, liquid/solids mixing, heating/cooling, homogenization, and raw material addition. An advantage of batch processing is that it requires only one piece of equipment to produce a complete batch of product.
Present batch processing methods are not without their disadvantages, however. Firstly, as the batch size increases, the batch processing equipment escalates in complexity and cost. Additionally, there typically is less control over processing parameters, such as temperature and particle distribution in a batch process relative to that in a continuous process. Furthermore, overall processing efficiency decreases.
The batch reactor also presents scale-up problems in the transition from a pilot batch reactor to a production scale version. It is difficult to correlate mixing speeds and times, heating and cooling rates, and other parameters for batch reactors that vary in size, shape, and geometry. Often, development work performed for a pilot batch reactor must be duplicated during production version scale-up.
Another disadvantage of batch reactors is the limited range of batch sizes possible. This limits the flexibility of batch processes and often requires duplicate equipment to meet production needs.
Lastly, a batch reactor is difficult to retrofit with technological improvements. For example, replacing an in-tank homogenizer in a batch reactor with a new and improved in-line homogenizer may be difficult or impossible. This is a significant drawback because a batch reactor may quickly become obsolete due to its inability to be retrofitted with improved components.
Therefore, both continuous in-line processes and present batch processes are inadequate to meet current processing requirements. The present inventors have discovered a recirculatory batch process (RBP) and related equipment which achieve the advantages of a continuous in-line processing system, i.e., minimal scale-up difficulties, reasonable cost, lack of batch size dependency, and adaptability for retrofitting, but in a batch process system.